One of the common problems suffered by contact lens wearers is an infection with bacteria. As one of countermeasures, a method of suppressing adhering of bacteria during preservation of contact lenses by containing antimicrobial components in a cleaning/storage solution for the contact lenses (for example, see the Patent Document 1). However, the method was not advantageous in that the antimicrobial components were easily washed away when the contact lenses taken out of the cleaning/storage solution were simply washed with water, thereby failing to obtain a sufficient effect of controlling infections with bacteria while the contact lenses were being worn.
Apart from the foregoing method, there was such an approach that an antimicrobial activity was imparted to a material of the contact lens. For example, the Patent Documents 2 and 3 recite antimicrobial contact lenses obtained by copolymerizing a non-silicone hydrogel material with a quaternary ammonium salt monomer having an antimicrobial activity. However, these contact lenses, in which the non-silicone hydrogel is used as the material, unfavorably could not obtain such a high degree of oxygen permeability that was necessary for the continuous wear of the contact lenses.
Further, the Patent Document 4 recites that a silicone hydrogel material having the high oxygen permeability is copolymerized with the quaternary ammonium salt monomer. However, the silicone compound used in the relevant Document is a silicone macromer having a large molecular weight, which is poor in solubility in the ammonium salt monomer having a high hydrophilicity. As a result, it was not possible to obtain a transparent polymer.    PATENT DOCUMENT 1: Japanese Translations of PCT Application No. 2006-509532    PATENT DOCUMENT 2: Japanese Patent Application Laid-Open No. 06-337378    PATENT DOCUMENT 3: Japanese Patent Application Laid-Open No. 63-30820    PATENT DOCUMENT 4: Japanese Translation of PCT Application No. 11-502949